Various approaches exist for providing RF power to dynamic loads. RF generators provide power to dynamic loads typically at frequencies between about 400 kHz and about 200 MHz. Frequencies used in some scientific, industrial and medical applications are approximately 2 MHz, 13.56 MHz and 27 MHz.
As shown in FIG. 1A, one system 100 for providing RF power to dynamic loads (i.e., a plasma load 140) involves a fixed frequency RF generator 110 and a two-axis tunable matching network 120 connected by a 50Ω transmission line 130. The tunable matching network 120 includes a series motorized vacuum variable capacitor 122 and inductor 124 and a shunt motorized vacuum variable capacitor 126. The algorithm used to determine the series and shunt capacitance is based on impedance measurements typically made using a magnitude and phase detector 150. Independent power control is based on power measurements at the RF generator 110. The power control loop 160 and impedance control loop 162 are independent.
As shown in FIG. 1B, another system 100′ for providing RF power to dynamic loads involves a fixed element matching network 120′ fed by an RF generator 110 and connected by a 50Ω transmission line 130. The fixed element matching network 120′ includes a series capacitor 122 and inductor 124 and a shunt capacitor 126. The frequency of the RF generator 110 can be tuned to a certain range (e.g., 13.56 MHz±5%). The RF generator 110 frequency command is based on the value of voltage standing wave ratio (VSWR). The independent power loop and VSWR (impedance) control loop 160′ are based on measurements at the output of the RF generator 110.
As shown in FIG. 1C, another system 100″ for providing RF power to dynamic loads involves an integrated RF generator-impedance matching network 120″. The RF generator-impedance matching network 120″ includes a series capacitor 122 and inductor 124 and a plurality of shunt capacitor 126a . . . 126n. The shunt capacitor 126a . . . 126n are coupled to a switching circuit 127a . . . 127n that couples and decouples the capacitors 126 to ground. The power control and frequency control 160″ of the system 100″ are not conducted simultaneously.